1. Field of the Invention
This invention relates to a fuel injection control system for injecting fuel into an air intake passage of an internal combustion engine, and more particularly to such a system including a heater for heating the intake air which improves the composition of the combustion gas at engine cold start.
2. Description of the Prior Art
When a cold engine is started, a part of the fuel injected by the fuel injection valves fails to vaporize because of the low temperature of the intake air and the cylinder walls and this fuel adheres to the walls of the intake passage and the cylinders. The resulting incomplete fuel combustion could produce harmful components that foul the combustion gas. Conventional ways proposed for coping with this problem include that of advancing the fuel injection timing so as to provide a longer period for the injected fuel mist to vaporize and that taught by Japanese Laid-open Utility Model Publication No. 56-127866 of heating the air-fuel mixture.
However, when the injection timing is advanced and, in addition, the air-fuel mixture is heated, a part of the air-fuel mixture vaporized by the heating condenses on the cold intake passage wall while it is resident in the intake passage prior to the cylinder intake stroke. As a result, no substantial improvement in the combustion gas composition is achieved.
It is therefore an object of this invention to provide a fuel injection control system for an internal combustion engine including a heater for heating the intake air which improves the composition of the combustion gas emitted even at the time of cold engine starting.